1. Field of the Invention
The present invention relates generally to the control of haptic feedback devices.
2. Description of the Related Art
Humans interface with electronic and mechanical devices in a variety of applications, and the need for a more natural, easy-to-use, and informative interface is a constant concern. One such application is interacting with computer-generated environments such as games, simulations, and application programs. Computer input devices such as mice and trackballs are often used to control a cursor within a graphical environment and provide input in these applications. In portable computer or electronic devices, such as laptop computers or personal digital assistants (PDAs), mice typically have too large a workspace to be practical. A popular device for portable computers are “touchpads,” or touchscreens, which are small rectangular, planar pads that sense the location of a pointing object by any of a variety of sensing technologies.
In some interface devices, haptic feedback is also provided to the user. These types of interface devices can provide physical sensations which are felt by the user manipulating a user object (which may be referred to as a manipulandum) of the interface device. One or more motors or other type of actuators are coupled to the device housing or manipulandum and are connected to the controlling computer system. The computer system controls forces output by the actuators in coordination with displayed events. The computer system can thus convey physical force sensations to the user in conjunction with other supplied feedback as the user is grasping or contacting the interface device or manipulatable object or manipulandum.
In many haptic feedback devices, the haptic feedback takes the form of vibrations, jolts, or pulses output on the housing and/or manipulandum to be thus experienced by the user as tactile sensations providing additional feedback and enhancing the interaction experience. For example, many gamepad devices include a spinning eccentric mass that creates inertial vibrations on the gamepad or related objects. Other devices, such as the I-Feel Mouse from Logitech Corporation, provide inertial vibrations using a linearly-moving mass. Still other devices may vibrate a housing or object by impacting or directly moving the housing or object with the actuator, which may be for example a piezoelectric device or the like.
One problem with current haptic feedback devices is that tactile sensations output to the user tend to be more effective in particular frequency ranges and are less effective in other frequency ranges, thus causing haptic sensations to feel uneven and inconsistent to the user over broad frequency ranges, and requiring inconsistent amounts of drive power and input. The inconsistencies are functions of many variables, including the mechanics of the device being vibrated and the various components thereof, based in part on the interactions and arrangements of these components. Inherently, each such device has one or more resonance frequencies at which the device resonates, providing optimal response to induced actuation such as vibration at said resonance frequency or frequencies. The resonance frequency can change and depends on factors such as temperature and other physical parameters, component arrangement and interaction, and interaction by the user, which can vary in location and intensity and thereby impart commensurate variation in the resonance frequency of the device.
In related U.S. Pat. No. 7,154,470, whose FIG. 1 is reproduced herein, a desired haptic frequency is superimposed on the resonance frequency of the haptic device. In this manner, the desired haptic effect can be imparted to the device (and user) by using the resonance frequency as the optimum “vehicle” to convey this effect, since the device vibrates or resonates best at this resonance frequency and the most efficient response by the device can thus be achieved. In FIG. 1, a modulation circuit 10 includes a reference oscillator 11 serving to provide the reference signal (at or near resonance) to an envelope modulator 12. A microcontroller 14 is coupled to the envelope modulator 12, providing an envelope signal 13 thereto, thereby enabling the envelope modulator to modulate the reference signal from reference oscillator 11 based on the envelope signal. The output of the envelope modulator 12, having the form of a modulated command signal 16, is then passed through a low pass filter 15, whose output is provided to an inverter 17 and, in the from of an envelope modulated signals 18, to a transducer/amplifier 19. The transducer/amplifier 19 relies for instance on pulse-width modulation (PWM) techniques and is coupled to a portion (not shown) of a user interface device, such as a housing of a touchpad or a joystick or similar device as described above, operating to impart haptic forces to said portion for providing tactile feedback based on the signal processed by the modulation circuit 10.
While the modulation circuit of FIG. 1 provides adequate control of a haptic force signal and can be readily tuned to a resonant frequency of the device, in some cases more versatility may be desired, for instance when the resonant frequency is changeable due to one or more of the factors discussed above, including variations in user interaction, in ambient temperature, and so on. In addition, it may be desirable to manage the excitation signal provided to the haptic device so as to remove spurious or unwanted components thereof, such as those that may produce unwanted audible effects. On the other hand, in some instances the opposite may be desired—that is, the provision of both audible and haptic feedback may be intended. In either case, the ability to tailor the excitation signal driving the actuator to achieve the desired response—haptic only, or haptic-plus-audio (or even audio only)—would provide a valuable advantage. Further, the elimination of some of the components of the modulation circuit can yield size and cost savings.